Bubble formation in organic light-emitting diodes

Bubbles in organic light-emitting diodes can be formed from gas release due to Joule heating effect at localized electrical shorts during operation, w hich could be simulated by a rapid thermal annealing. The gases in the bubb les consist of not only adsorbed moistures but also the decomposed organic species, which are detected in situ in an ultrahigh vacuum chamber. In the device of Al/tris-(8-hydroxyquinoline) aluminum (Alq/N,N'-diphenyl-N.N'-bis -{3-methylphenyl}{1,1'biphenyl}-4,4'-diamine/indium tin oxide (ITO), the ga ses released from ITO surface were mainly of adsorbed moistures, while thos e released from the organic layers were of both the decomposed products fro m Alq and the trapped moistures. The decomposition of Alq could not be easi ly avoided if there were severe localized electrical shorts in the devices. (C) 2000 American Institute of Physics. [S0021-8979(00)00613-7].